For example, U.S. Pat. No. 6,339,337 B1 discloses an infrared ray test for a semiconductor chip. The test is conducted by irradiating an infrared ray onto a bottom surface of a semiconductor chip, receiving the infrared ray reflected from a bonding pad, and displaying the image of the bonding pad on a monitor. The image obtained from the infrared ray has information whether the bonding pad itself or a portion of the silicon substrate underlying the bonding pad has a defect or whether or not there is a deviation of the bonding pad with respect to the bump.
Chinese utility model CN 2791639 (Y) discloses a detecting device, which is mainly used for detecting internal defects of semiconductor material of which the band gap is larger than 1.12 eV. The detecting device for detecting internal defects of semiconductor material is composed of an optical microscope, an infrared CCD camera, video cable, a simulation image monitor, a digital image collection card, a computer and analysis process and display software. Additionally, EP 2699071 A2 disclose an optoelectronic method for recording a heat diagram from the temperature distribution of land in which an infrared line scan system is used in an aircraft. The apparatus utilizes a rotary scanning mirror system receiving heat radiation through windows. The mirror system has four reflecting sides and is rotated about an axis by an electric motor. The radiation is directed by mirrors to an IR lens and then to a row of optoelectronic receiver elements. The row of receiver elements is parallel to the axis of rotation of the mirror system, each receiver element being individually connected by a lead and an amplifying device to a corresponding one of a number of luminescent diodes.
U.S. Pat. No. 8,154,718 B2 discloses a device to analyze micro-structured samples of a wafer. The aim of the device is to increase the possible uses of said devices, i.e. particularly in order to represent structural details, e.g. of wafers that are structured on both sides, which are not visible in VIS or UV because coatings or intermediate materials are not transparent. IR light is used as reflected light while creating transillumination which significantly improves contrast in the IR image, among other things, thus allowing the sample to be simultaneously represented in reflected or transmitted IR light and in reflected visible light.
Typical defects are side cracks created by the dicing process or embedded cracks created by internal stress in the device between the dielectric layer and the silicon structure.
FIG. 1 shows a prior art method for finding side defects 9 in a semiconductor device 2 by doing a four sided or a five sided inspection. The semiconductor device 2 has a first side face 31, a second side face 32, a third side face 33, a fourth side face 34, a top face 4 and a bottom face 5. In the setup of FIG. 1 a camera 6 with a lens 7 looks to the bottom face 5 of the semiconductor device 2. A mirror 8 is arranged under 45 degrees with each of the first side face 31, the second side face 32, the third side face 33 and the fourth side face 34 of the semiconductor device 2, respectively. In FIG. 1 only the mirrors 8 arranged with respect to the second side face 32 and the fourth side face 34 of the semiconductor device 2 are shown.
The setup of FIG. 1 is used to obtain an image 10 (see FIG. 2) of the first side face 31, the second side face 32, the third side face 33, the fourth side face 34 and the bottom face 5, respectively. Additionally, the setup of FIG. 1 has significant drawbacks. The optical length 11 of the bottom face 5 view differs from the optical length 12 of the first side face 31 view, the second side face 32 view, the third side face 33 view and the fourth side face 34 view. Therefore, the focus is always a trade-off between focus on the bottom face 5 of the semiconductor device 2 and focus on the first side face 31, the second side face 32, the third side face 33 and the fourth side face 34, respectively. Additionally, the image resolution of the four-sided view requires a large field of view and this will limit the pixel resolution that can be used. For side views <10μm there is no working setup available, even by using a high resolution camera of 20 or 25 megapixels. Therefore it is not possible to have good focus and a high resolution in order to discriminate a real defect from non-critical contamination.
FIG. 3 is another embodiment of a prior art set-up for detecting interior defects 9 (side defects) by looking onto the top face 4 of a semiconductor device 2. For detecting interior defects 9 (that are invisible from the outside) there is no solution for high volume inspection. There is a slow method by using IR light 13 and optics 14 and looking to the back face of the semiconductor device 2 (“IR back view”). A camera 6 detects the IR-light 15 returning from the semiconductor device 2. A schematic representation of an image 16, obtained with the setup of FIG. 3 is shown in FIG. 4. The “IR back view” method with IR light 13 for detecting the interior defects 9 has drawbacks as well. First of all the method is slow. It only exists as manual, low volume method. If one wanted to automate this and make it faster there is an important limitation in the size and the number of pixels of the available IR cameras 6. Additionally, it only works for a limited set of devices where there is a bare silicon side to apply the IR light. An increasing number of devices have a coating to protect the device, which coating is not transparent for IR light. A further drawback is the signal to noise ratio. The top face 4 of the semiconductor device 2 will also create a reflection which makes it hard to distinguish a top defect from an interior defect 9.
This prior art method, described above, has significant drawbacks by inspecting five sides of a work piece (singulated semiconductor device). One drawback is the differing focus between the side face and the bottom face of the work piece. The optical length is different for bottom and side view, therefore the focus is always a trade-off between focus on the bottom of the work piece and focus on the edges (side faces) of the work piece. A further drawback is the image resolution. A view of the four side faces requires a large field of view and this will limit the pixel resolution that can be used.